1. Field of the Invention
The present invention generally relates to a method of manufacturing a semiconductor device, and more particularly to a patterning method using chemically amplified resist.
2. Description of the Related Art
In recent years, shortening the exposure wavelength in a lithographic process has advanced along with manufacturing semiconductor elements into microscopic sizes. KrF excimer lasers or ArF eximer lasers are now mainly employed as Deep-UV (DUV).
Compared to the conventional lithography process such as i-line lithography, the use of DUV as exposure wavelength has a problem of being easily subject to interference from substrate reflection. Therefore, such reflection and interference are often prevented by forming a reflection preventing film called BARC (Bottom Anti Reflective Coating) under the resist.
Further, the use of DUV often requires the employment of an exposure system of high numerical aperture for enhancing resolution. Therefore, obtaining sufficient focal depth would be difficult, and forming a thin layer resist would be a requirement. A method has been developed for solving the problem of etch resistance in a case of forming a thin layer resist, in which a film having a composition different from that of the resist is formed under the resist, and is used as a mask for etching.
Accordingly, employment of multi-layered resist is presently considered to be an effective technique.
Presently, a chemically amplified resist is typically used for enhancing resist resolution and sensitivity. A chemically amplified resist added with an acid generating agent which generates acid in the resist when exposed to light, creates further acid from catalytic reaction, and changes the resist to an alkali soluble molecular structure. This is a case of a positive type resist, but a negative type resist exists as well.
Using the chemically amplified resist, however, may change patterning size and resolution depending on the degree in the diffusion of acid. Patterning could, for example, be affected by acid or base formed in the resist interface.
For example, in a case of forming the BARC under the resist, some resist may experience defective formation called skirt trailing caused during pattern forming. Skirt trailing is a phenomenon where resist slantingly remains at a bottom portion of a pattern aimed for removal. This is a phenomenon where the acid generated by the acid generating agent contained in the resist is deactivated by the constituent inside the BARC.
A three layer process will hereinafter be described as an example of a process using a multi-layered resist. The three layer process is a method of, for example, forming an insulation film such as an SOG film under the resist, then forming a polymer film such as novolac resin under the aforementioned SOG film, and then forming a pattern upon a targeted processing film under the polymer film. That is, an insulating film is etched and patterned according to a pattern of a topmost resist formed thereon, then, a polymer film is etched using the insulating film as a mask, and then, an insulating film (e.g. silicon oxide film), which is a targeted processing film under the polymer film, is dry-etched to thereby transfer the pattern of the polymer film thereon. The polymer film being the bottom-most layer serves as the BARC for preventing reflection. In recent years, this method has become widely used since the topmost layer of resist can be formed into a thin layer.
Nevertheless, in the foregoing three layer process, similar to the foregoing case of using a BARC, the acid created by the chemically amplified resist formed on the top-most portion is deactivated by the constituent inside the SOG film serving as an underlayer beneath the chemically amplified resist, to thereby cause the aforementioned phenomenon of skirt trailing.
Therefore, in the current situation, adding of BARC or adding of acid generating agent to the SOG film is performed in order to supplement the deactivated acid and to adjust the formation of patterns.
However, in a case where an acid generating agent is added to a film serving as an underlayer for the resist, acid density will increase, for example, at the interface between the BARC and the resist, or at the interface between the SOG film and the resist, and furthermore, remaining acid would remove a protective group of the resin and become alkali soluble, to thereby cause a problem of intrusion at the resist interface. Using a negative type resist, on the other hand, faces problems such as skirt trailing at the bottom of the resist, or remaining of scum.
Furthermore, adding the acid generating agent to the SOG film may deteriorate the adhesiveness between the SOG film and the resist. Furthermore, the acid generated from the acid generating agent cannot be evenly distributed to the SOG film, and therefore, the pattern formed on a surface thereof could be scattered. Furthermore, the efficiency in the generation of acid may change since the amount of exposure changes in accordance with the coverage of a reticle, and therefore, optimizing the amount of the acid generating agent is extremely difficult. Furthermore, much time is required for adding and adjusting the acid generating agent to the SOG film when the resist is changed.
FIGS. 1A and 1B show an example where a resist pattern has collapsed when patterning with the three layer process of the foregoing conventional art. The patterns denoted as a and b in FIGS. 1A and 1B are separated from the substrate targeted for processing, to thereby cause a phenomenon called pattern-collapse. The remaining acid at the interface between the resist and the underlayer for the resist is considered to be the cause of this phenomenon.
It is therefore a general object to provide a method of manufacturing a semiconductor device for beneficially solving the aforementioned problems.